This invention relates to a fluidized bed heat exchanger and, more particularly, to such a heat exchanger in which effluent gases from the bed are passed over a plurality of heat exchange tubes to add heat to water flowing through the tubes.
The use of fluidized beds has long been recognized as an attractive means of generating heat. In these arrangements air is passed through a bed of particulate material which includes a mixture of inert material, a fuel material such as high sulfur, bituminous coal and, usually, adsorbent material for the sulfur released as a result of the combustion of the coal. As a result of the air passing through the bed, the bed is fluidized which promotes the combustion of the fuel. The basic advantages of such an arrangement are many and include a relatively high heat transfer rate, a substantially uniform bed temperature, combustion at relatively low temperatures, ease of handling the fuel materials, a reduction in corrosion and boiler fouling and a reduction in boiler size.
It has been suggested to provide a tube bank in connection with the above-described type of fluidized bed which tube bank normally extends between two drums for circulating water therebetween so that, when the mixture of the combustion gases from the fluidized bed and the excess air passing through the fluidized bed (with said mixture hereinafter being referred to as "effluent gases") is passed over the tube bank, heat from the effluent gases is added to the water in the tubes. However, in these type arrangements, a substantial amount of combustible matter and/or other reactant, in the form of solid dust-like particulate material is normally carried away as particles in the effluent gases. This presents problems especially in connection with the use of tube banks since the solid particulate material tends to collect on and build up on the tubes causing erosion and a reduction in efficiency.
Although it has been suggested to separate this particulate material from the effluent gases, it is often done by external cyclone separators, or the like, which, in addition to being relatively expensive, must be located externally of the heat exchanger thus requiring a system for discharging the effluent gases externally of the heat exchanger and to the cyclone separator.